Heat pipe

ABSTRACT

A heat pipe includes a hollow elongated casing, which defines therein an enclosed chamber, a working fluid filled in the enclosed chamber; and a wick, which is formed on the inside wall of the casing around the enclosed fluid chamber and has two parts that have different porosities.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to heat transferring devices andmore particularly, to a high-performance heat pipe of which the wick hasdifferent porosities at different parts for different functions.

2. Description of the Related Art

A conventional heat pipe generally comprises a hollow metal tube, whichhas the both ends closed, a working fluid, for example, pure waterfilled in the metal tube, and a wick formed of copper powder on theinside wall of the metal tube by sintering. The wick has pores forabsorbing the working fluid.

When one end of the heat pipe touched a heat source, the pure water atthe heating end is vaporized, and produced steam is quickly dissipatedto the other end, namely, the cold end where steam is condensed intowater to release latent heat. At this time, condensed water flows backto the heating end through the pores in the wick, completing one thermalcycle. By means of the alternation of the working fluid between theliquid phase and the gas phase, the heat pipe transfers a big amount ofheat energy.

To facilitate fabrication, the wick of a heat pipe is made having auniform porosity. However, the porosity has a great concern with theperformance of the heat pipe. A wick having a relatively lower porosityprovides a relatively better capillary effect, however its flow pathfunction for carrying the working fluid is relatively poorer. On thecontrary, a wick having a relatively higher porosity provides arelatively better flow patch function for carrying the working fluid,however its capillary effect is relatively weaker. Therefore, it is animportant work how to maintain the capillary effect of the wick whileimproving the flow path function for carrying the working fluid.

SUMMARY OF THE INVENTION

The present invention has been accomplished under the circumstances inview. It is the main object of the present invention to ahigh-performance heat pipe, which uses a wick that provides asatisfactory capillary effect and flow path function for carrying theworking fluid.

To achieve this and other objects of the present invention, the wick ofthe heat pipe has at least two different porosities to provide asatisfactory capillary effect and flow path function for carrying theworking fluid, thereby improving the thermal transfer performance of theheat pipe.

In one embodiment of the present invention, the wick has axially dividedmultiple parts that have different porosities. In another embodiment ofthe present invention, the wick has radially divided multiple parts thathave different porosities. Preferably, the wick has two parts, namely,the first part that has a porosity within about 55%-60%, and the secondpart that has a porosity within about 65%-80%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. I is a schematic sectional view of a heat pipe according to thepresent invention.

FIG. 2 is a schematic sectional view of an alternate form of the heatpipe according to the present invention.

FIG. 3 is a schematic sectional view of another alternate form of theheat pipe according to the present invention.

FIG. 4 is a sectional view taken along line 4-4 of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a heat pipe in accordance with the presentinvention is shown comprising a casing 10, a working fluid 20, and awick 30.

The casing 10 is a metal tube having the both ends closed and definingtherein an enclosed chamber 11. The working fluid 20 is disposed in theenclosed chamber 11. According to this embodiment, the working fluid 20is pure water. Other fluids may be selectively used as a substitute.Further, the casing 10 has a heating end 12 and a cooling end 14.

The wick 20 is formed of copper powder on the inside wall of the casing10 by sintering, having axially divided three parts, namely, the firstpart 32, the second part 34, and the third part 36. These three parts32, 34 and 36 have different porosities. The porosity of the first part32 of the wick is 55%. The porosity of the second part 34 of the wick is80%. The porosity of the third part 36 of the wick is 60%.

When the heating end 12 of the casing 10 touched a heat source, theworking fluid 20 is vaporized, and produced steam flows along thechamber 11 to the cooling end 14 where steam is condensed into liquid.At this time, the third part 36 provides a better capillary effect toabsorb the working fluid 20 around the cooling end. When the workingfluid 20 is returning to the heating end 12, and the second part 34provides a better flow path function to reduce the resistance to thereverse flowing of the working fluid 20. Further, the first part 36 alsoprovides a better capillary effect to absorb the working fluid 20 fromthe second part 34 to the heating end 12.

Because the first, second and third parts 32, 34 and 36 of the wick 30have different porosities, the wick 30 provides a better flowing pathfunction and a satisfactory capillary effect, achieving a highperformance in heat transfer.

Further, alloy powder of copper and silver or other suitable materialsmay be selectively used for sintering into the desired wick 30 insteadof copper powder. A porosity ranging from 55%-60% provides a bettercapillary effect. A porosity ranging from 65%-80% provides a better flowpath function. In actual fabrication, the porosity of each part of thewick 30 may be changed subject to actual requirements, and each part maybe made having different porosities gradually increased from one end tothe other.

FIG. 2 shows an alternate form of the heat pipe according to the presentinvention. According to this embodiment, the heat pipe comprises acasing 10, a working fluid 20, and a wick 30. The wick 30 is axiallydivided into a first part 32 and a second part 34. The porosity of thefirst part 32 is 75%. The porosity of the second part 34 is 55%. Bymeans of this design, the second part 34 provides a better capillaryeffect, and the first part 32 provides a better flow path function.

FIGS. 3 and 4 show another alternate form of the heat pipe according tothe present invention. According to this embodiment, the heat pipecomprises a casing 10, a working fluid 20, and a wick 30. The wick 30 isradially divided into a first part 32 and a second part 34. The firstpart 32 is disposed at an outer side and bonded to the inside wall ofthe casing 10. The porosity of the first part 32 is 70%. The second part34 is disposed at an inner side and bonded to the first part 32. Theporosity of the second part 34 is 58%. The second part 34 provides abetter capillary effect to absorb the working fluid 20. The first part32 provides a better flow path function to reduce the resistance to thereverse flowing of the working fluid 20. Therefore, the heat pipeprovides a better flowing path function and a satisfactory capillaryeffect, achieving a high performance in heat transfer.

Although particular embodiments of the invention have been described indetail for purposes of illustration, various modifications andenhancements may be made without departing from the spirit and scope ofthe invention. Accordingly, the invention is not to be limited except asby the appended claims.

1. A heat pipe comprising: a hollow elongated casing, said casing defining therein an enclosed chamber; a working fluid disposed in said enclosed chamber; and a wick formed on an inside wall of said casing; wherein said wick has a first part and a second part, said first part and said second part have different porosities.
 2. The heat pipe as claimed in claim 1, wherein said first part of the wick has a porosity within 55%-60%; said second part of the wick has a porosity within 65%-80%.
 3. The heat pipe as claimed in claim 2, wherein said casing has a heating end and a cooling end opposite said heating end; said first part of the wick is located at said heating end, and said second part is located at said cooling end.
 4. The heat pipe as claimed in claim 2, wherein said casing has a heating end and a cooling end opposite to said heating end; said wick further has a third part, said third part having a porosity within about 55%-60%, said first part of the wick being disposed at said heating end, said third part of the wick being disposed at said cooling end, said second part of the wick being located between said first part and said third part of the wick.
 5. The heat pipe as claimed in claim 1, wherein said wick is sintered from copper powder or alloy powder of copper and silver.
 6. The heat pipe as claimed in claim 1, wherein said first part and said second part of the wick are axially arranged in a line.
 7. The heat pipe as claimed in claim 1, wherein said first part of the wick is bonded to the inside wall of said casing, and said second part of the wick is bonded to said first part of the wick. 